import java.util.Scanner;

public class QQ {
    public static void main(String[] args){
        int a;
        System.out.println("输入半径");
        Scanner A = new Scanner(System.in);
        a = A.nextInt();
        System.out.println(aykl( a));
    }
    public static double aykl(int a){
        double pi=Math.PI;
        return(pi*a*a);

    }
}
